Finfet with constrained source-drain epitaxial region

ABSTRACT

A method includes forming a plurality of fins on a substrate, conformally depositing a nitride liner above and in direct contact with the plurality of fins and the substrate, removing a top portion of the nitride liner above the plurality of fins to expose a top surface of the plurality of fins, forming a gate over a first portion of the plurality of fins, a second portion of the plurality of fins remains exposed, forming spacers on opposite sidewalls of the nitride liner on the second portion of the plurality of fins, removing the second portion of the plurality of fins to form a trench between opposing sidewalls of the nitride liner, and forming an epitaxial layer in the trench, the lateral growth of the epitaxial layer is constrained by the nitride liner to form constrained source-drain regions.

BACKGROUND

The present invention generally relates to semiconductor manufacturingand more particularly to fin field effect transistor (FinFET) deviceshaving constrained source-drain epitaxial regions.

Complementary Metal-oxide-semiconductor (CMOS) technology is commonlyused for fabricating field effect transistors (FETs) as part of advancedintegrated circuits (IC), such as CPUs, memory, storage devices, and thelike. Most common among these may be metal-oxide-semiconductor fieldeffect transistors (MOSFET). In a typical MOSFET, a gate structure maybe energized to create an electric field in an underlying channel regionof a substrate, by which charge carriers are allowed to travel between asource region and a drain region. As ICs continue to scale downward insize, fin field effect transistors (FinFETs), sometimes referred to astri-gate structures, may be potential candidates for the 14 nm nodetechnology and beyond, primarily because FinFETs may offer betterperformance than planar FETs at the same power budget. FinFETs arethree-dimensional (3D), fully depleted MOSFET devices having a pluralityof fins formed from the substrate material. The gate structure may belocated over the fins substantially covering the channel region, theportion of the fins not covered by the gate structure may define thesource-drain regions of the device. Such architecture may allow for amore precise control of the conducting channel by the gate structure,significantly reducing the amount of current leakage when the device isin off state.

SUMMARY

According to an embodiment of the present disclosure, a method includes:forming a plurality of fins on a substrate, forming a gate over a firstportion of the plurality of fins, a second portion of the plurality offins remains exposed, forming spacers on opposite sidewalls of thesecond portion of the plurality of fins, removing the second portion ofthe plurality fins to form a trench between the spacers, and forming anepitaxial layer in the trench, lateral growth of the epitaxial layer isconstrained by the spacers.

According to another embodiment of the present disclosure, a methodincludes: forming a plurality of fins on a substrate, conformallydepositing a nitride liner above and in direct contact with theplurality of fins and the substrate, removing a top portion of thenitride liner above the plurality of fins to expose a top surface of theplurality of fins, forming a gate over a first portion of the pluralityof fins, a second portion of the plurality of fins remains exposed,forming spacers on opposite sidewalls of the nitride liner on the secondportion of the plurality of fins, removing the second portion of theplurality of fins to form a trench between opposing sidewalls of thenitride liner, and forming an epitaxial layer in the trench, lateralgrowth of the epitaxial layer is constrained by the nitride liner toform constrained source-drain regions.

According to another embodiment of the present disclosure, a structureincludes: a plurality of fins on a substrate, and a gate over a firstportion of the plurality of fins, a second portion of the plurality offins not covered by the gate comprises an epitaxial layer geometricallyconstrained by a pair of spacers located on opposite sidewalls of thesecond portion of the plurality of fins.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the invention solely thereto, will best be appreciatedin conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a semiconductor structure depictingforming a plurality of fins, according to an embodiment of the presentdisclosure;

FIG. 2 is a cross-sectional view of the semiconductor structuredepicting forming a gate and a gate cap, according to an embodiment ofthe present disclosure;

FIG. 2 a is a side view of the semiconductor structure, according toFIG. 2;

FIG. 3 is a cross-sectional view of the semiconductor structuredepicting forming sidewall spacers, according to an embodiment of thepresent disclosure;

FIG. 4 is a cross-sectional view of the semiconductor structuredepicting removing the plurality of fins, according to an embodiment ofthe present disclosure;

FIG. 4 a is a cross-sectional view of the semiconductor structuredepicting partially removing the plurality of fins, according to anembodiment of the present disclosure;

FIG. 5 is a cross-sectional view of the semiconductor structure,depicting growing an epitaxial layer, according to an embodiment of thepresent disclosure;

FIG. 6 is a cross-sectional view of the semiconductor structure,depicting forming an extended epitaxial region, according to anembodiment of the present disclosure;

FIG. 7 is a cross-sectional view of the semiconductor structure,depicting depositing a nitride liner over the plurality of fins,according to another embodiment of the present disclosure;

FIG. 8 is a cross-sectional view of the semiconductor structure,depicting depositing a dielectric layer, according to another embodimentof the present disclosure;

FIG. 9 is a cross-sectional view of the semiconductor structure,depicting removing the nitride cap, according to another embodiment ofthe present disclosure;

FIG. 10 is a cross-sectional view of the semiconductor structure,depicting forming a gate and a gate cap, according to another embodimentof the present disclosure;

FIG. 11 is a cross-sectional view of the semiconductor structure,depicting forming sidewall spacers, according to another embodiment ofthe present disclosure;

FIG. 12 is a cross-sectional view of the semiconductor structure,depicting removing the plurality of fins, according to anotherembodiment of the present disclosure;

FIG. 12 a is a cross-sectional view of the semiconductor structure,depicting partially removing the plurality of fins, according to anotherembodiment of the present disclosure;

FIG. 13 is a cross-sectional view of the semiconductor structure,depicting forming an epitaxial layer, according to another embodiment ofthe present disclosure; and

FIG. 14 is a cross-sectional view of the semiconductor structure,depicting forming an extended epitaxial region, according to anotherembodiment of the present disclosure.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention. In the drawings, like numbering representslike elements.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it may be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of this invention to thoseskilled in the art.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps, and techniques, in order to provide a thoroughunderstanding of the present invention. However, it will be appreciatedby one of ordinary skill of the art that the invention may be practicedwithout these specific details. In other instances, well-knownstructures or processing steps have not been described in detail inorder to avoid obscuring the invention. It will be understood that whenan element as a layer, region, or substrate is referred to as being “on”or “over” another element, it may be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” or “directly over” anotherelement, there are no intervening elements present. It will also beunderstood that when an element is referred to as being “beneath,”“below,” or “under” another element, it may be directly beneath or underthe other element, or intervening elements may be present. In contrast,when an element is referred to as being “directly beneath” or “directlyunder” another element, there are no intervening elements present.

In the interest of not obscuring the presentation of embodiments of thepresent invention, in the following detailed description, someprocessing steps or operations that are known in the art may have beencombined together for presentation and for illustration purposes and insome instances may have not been described in detail. In otherinstances, some processing steps or operations that are known in the artmay not be described at all. It should be understood that the followingdescription is rather focused on the distinctive features or elements ofvarious embodiments of the present invention.

In modern CMOS technologies, epitaxially grown materials may betypically used to form source-drain regions of FET devices since theymay provide strain and resistivity benefits. In FinFETs manufacturing,continuous scaling of semiconductor devices may translate in a tighterpitch between adjacent fins. Owing to the tighter pitch between adjacentfins, epitaxial films grown off the fin sidewalls may impose a lateralgrowth constraint on the source-drain regions of the device, which maynegatively affect device spacing and density requirements whenmaintaining unmerged devices is desired. Additionally, the epitaxialfilm forming a source-drain region of the FinFET device may extendlaterally to contact the epitaxial film forming an adjacent source-drainregion, which may result in an unwanted electrical short between twoadjacent source-drain regions.

According to embodiments of the present disclosure, by cladding the finsbetween sidewall spacers, embodiments of the present disclosure may,among other potential benefits, constrain lateral epitaxial growthduring formation of source-drain regions thereby reducing the distancebetween adjacent fins and potentially increasing device density andperformance.

The present invention generally relates to semiconductor manufacturingand more particularly to FinFET devices having constrained source-drainepitaxial regions. One way to constrain source-drain epitaxial regionsmay include forming sidewall spacers on opposing sides of a fin,removing the fin to create a trench between the sidewall spacers andepitaxially growing a new fin within the recess. One embodiment by whichto form constrained epitaxial source-drain regions is described indetail below by referring to the accompanying drawings in FIGS. 1-6.

Referring now to FIG. 1, a semiconductor structure 100 may be formed orprovided, according to an embodiment of the present disclosure. In thedepicted embodiment, the semiconductor structure 100 may include aFinFET device. At this step of the manufacturing process, a plurality offin structures 14 (hereinafter “fins”) may be formed from a substrate 10of the semiconductor structure 100. In this embodiment, the substrate 10is a bulk semiconductor substrate which may be made from any of severalknown semiconductor materials such as, for example, silicon, germanium,silicon-germanium alloy, carbon-doped silicon, carbon-dopedsilicon-germanium alloy, and compound (e.g. III-V and II-VI)semiconductor materials. Non-limiting examples of compound semiconductormaterials include gallium arsenide, indium arsenide, and indiumphosphide. In the depicted embodiment, the substrate 10 may be made ofsilicon.

In other embodiments, the substrate 10 may be, for example, asemiconductor-on-insulator (SOI) substrate, where a buried insulatorlayer separates a base substrate from a top semiconductor layer. Thecomponents of the semiconductor structure 100, including the fins 14,may generally be formed in the top semiconductor layer.

The fins 14 may be formed from the substrate 10 using knownphotolithography and etch processes. In an exemplary embodiment, thefins 14 may be formed using a sidewall image transfer (SIT) technique.In embodiments in which the fins 14 may be formed from a bulksemiconductor substrate, the fins 14 may be isolated from one another byregions of a dielectric material such as, for example, shallow trenchisolation (STI) regions 12. It should be noted that, while theembodiment depicted in FIG. 1 includes five fins 14, any number of finsmay be formed from the substrate 10. In one exemplary embodiment, thefins 14 may have a height h ranging from approximately 5 nm toapproximately 200 nm, a width w ranging from approximately 5 nm toapproximately 25 nm and may be separated by a pitch p ranging fromapproximately 20 nm to approximately 100 nm.

Referring now to FIGS. 2-2 a, a gate electrode 22 (hereinafter referredto as “gate”) may be formed over a portion of the fins 14. In thisembodiment, FIG. 2 a is a side view of FIG. 2 taken along line A-A′.Exposed portions 16 of the fins 14 may consist of regions of the fins 14not covered by the gate structure 22 as illustrated in FIG. 2 a. Theportion of the fins 14 covered by the gate 22 may be referred to as achannel region. It should be noted that the semiconductor structure 100may be fabricated using either a replacement metal gate (RMG) or gatelast process flow, or a gate first process flow. For illustrationpurposes only, without intent of limitation, the embodiment describedbelow uses and details a gate first process flow.

The gate 22 may be generally formed above a gate dielectric (not shown).The gate 22 may include, for example, Zr, W, Ta, Hf, Ti, Al, Ru, Pa,metal oxide, metal carbide, metal nitride, transition metal aluminides(e.g. Ti3Al, ZrAl), TaC, TiC, TaMgC, and any combination of thosematerials. In one embodiment, the gate 22 may include tungsten (W). Thegate 22 may be deposited by any suitable technique known in the art, forexample by chemical vapor deposition (CVD), atomic layer deposition(ALD), physical vapor deposition (PVD), molecular beam deposition (MBD),pulsed laser deposition (PLD), or liquid source misted chemicaldeposition (LSMCD). The gate dielectric may include any suitableinsulating material such as, for example, oxide, nitride, oxynitride orsilicate including metal silicates and nitrided metal silicates. In oneembodiment, the gate dielectric may include an oxide such as, forexample, SiO₂, HfO₂, ZrO₂, Al₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃, andmixtures thereof. The gate dielectric may be formed by any suitabledeposition technique known in the art, including, CVD, plasma-assistedCVD, ALD, evaporation, reactive sputtering, chemical solution depositionor other like deposition processes. The physical thickness of the gatedielectric may vary, but typically may have a thickness ranging fromapproximately 0.5 nm to approximately 17 nm.

A gate cap 28 may be subsequently formed on top of the gate 22 using anysuitable deposition technique known in the art. The gate cap 28 mayinclude, for example, silicon oxide, silicon nitride, siliconoxynitride, boron nitride, or any suitable combination of thosematerials. In an exemplary embodiment, the gate cap 28 may have athickness ranging from approximately 30 nm to approximately 200 nm.

Referring now to FIG. 3, spacers 32 may be formed on opposite sidewallsof the gate 22 and opposite sidewalls of the fins 14. For illustrationpurposes only, without intent of limitation, only the spacers 32 onopposite sidewalls of the fins 14 are depicted in the drawings.

The spacers 32 may be made from an insulator material such as an oxide,nitride, oxynitride, silicon carbon oxynitride, silicon boronoxynitride, low-k dielectric, or any combination thereof. The spacers 32may be formed by known deposition and etching techniques. Formation ofthe spacers 32 may typically include full fin over etch by means of, forexample, a reactive ion etching (RIE) technique in order to expose theportion of the fins 14 not covered by the gate 22. In the depictedembodiment, minimal fin over etch is conducted in order to form thespacers 32 on opposite sidewalls of the fins 14. More specifically, thedeposited nitride material may be remove from all horizontal surfaces ofthe semiconductor structure 100 using an anisotropic etch. In variousembodiments, the spacers 32 may include one or more layers. It should beunderstood that while the spacers 32 are herein described in the plural,the spacers 32 may consist of a single spacer surrounding the fins 14.

Due to the etch process performed during formation of the spacers 32,the thickness of the gate cap 28 may be substantially less than intraditional CMOS process flow.

Referring now to FIGS. 4-4 a, the fins 14 (FIG. 3) may be removed frombetween the spacers 32, according to an embodiment of the presentdisclosure. The removal of the fins 14 (FIG. 3) may create a trench 44between the spacers 32. In embodiments in which the substrate 10 is anSOI substrate, the fins 14 (FIG. 3) may be partially removed asillustrated in FIG. 4 a. More specifically, in embodiments in which thesubstrate 10 is an SOI substrate, a portion of the fins 14 (FIG. 4 a)may remain at a bottom of the trench 44 to allow for the subsequentgrowth of an epitaxial layer.

The fins 14 (FIG. 3) may be selectively removed by means of any etchingtechnique known in the art including, but not limited to, reactive ionetching (RIE) or a wet etch processes. In an embodiment in which thefins 14 (FIG. 3) include silicon and the spacers 32 include a nitride, afluorine based RIE may be conducted to remove the fins 14 (FIG. 3). Itshould be noted that a portion of the fins 14 that is covered by thegate 22, otherwise referred to as the channel region, remains afterselectively removing the fins 14 from between the spacers 32.

Referring now to FIG. 5, an epitaxial layer 62 may be grown in thetrench 44 (FIG. 4), according to an embodiment of the presentdisclosure. The epitaxial layer 62 may replace the fins 14 (FIG. 3). Thetrench 44 (FIG. 4) between the spacers 32 may provide a template tore-grow the fins in the semiconductor structure 100 in a way such thatlateral epitaxial growth may not occur during the process of forming theepitaxial layer 62, and therefore producing laterally constrainedsource-drain regions 64. The epitaxial layer 62 may be grown directlyfrom the substrate 10 exposed at the bottom of the trench 44 (FIG. 4).In embodiments in which the substrate 10 is an SOI substrate, theepitaxial layer 62 may be grown directly from the portion of the fins 14(FIG. 4 a) remaining at the bottom of the trench 44 (FIG. 4 a). In suchembodiments, the portion of the fins 14 remaining at the bottom of thetrench 44 (FIG. 4 a) may serve as a seed layer for growing the epitaxiallayer 62.

The terms “epitaxial growth and/or deposition” and “epitaxially formedand/or grown” mean the growth of a semiconductor material on adeposition surface of a semiconductor material, in which thesemiconductor material being grown may have the same crystallinecharacteristics as the semiconductor material of the deposition surface.In an epitaxial deposition process, the chemical reactants provided bythe source gases are controlled and the system parameters are set sothat the depositing atoms arrive at the deposition surface of thesubstrate with sufficient energy to move around on the surface andorient themselves to the crystal arrangement of the atoms of thedeposition surface. Therefore, an epitaxial semiconductor material mayhave the same crystalline characteristics as the deposition surface onwhich it may be formed. For example, an epitaxial semiconductor materialdeposited on a {100} crystal surface may take on a {100} orientation. Insome embodiments, epitaxial growth and/or deposition processes may beselective to forming on semiconductor surfaces, and may not depositmaterial on dielectric surfaces, such as silicon dioxide or siliconnitride surfaces.

The epitaxial layer 62 may include any suitable semiconductor materialhaving a dopant concentration according to the characteristics of thesemiconductor structure 100.

For example, in one embodiment where the semiconductor structure 100 isan n-type field effect transistor (n-FET) device, the epitaxial layer 62may include a carbon-doped silicon (Si:C) material, where the atomicconcentration of carbon (C) may range from approximately 0.2% toapproximately 3.0%. The epitaxial layer 62 may be doped by any knownn-type dopant use in the fabrication of n-FET devices such as, forinstance, phosphorus or arsenic. In one embodiment, the dopantconcentration in the epitaxial layer 62 may range from approximately5×10¹⁹ cm⁻³ to approximately 2×10²¹ cm⁻³.

For example, in another embodiment where the semiconductor structure 100is a p-type field effect transistor (p-FET) device, the epitaxial layer62 may include a silicon germanium (SiGe) material, where the atomicconcentration of germanium (Ge) may range from approximately 10% toapproximately 80%. The epitaxial layer 62 may be doped by any knownp-type dopant use in the fabrication of p-FET devices such as, forinstance, boron. In one embodiment, the dopant concentration in theepitaxial layer 62 may range from approximately 5×10¹⁹ cm⁻³ toapproximately 2×10²¹ cm⁻³.

Examples of various epitaxial growth process apparatuses that may besuitable for use in forming the epitaxial layer 62 may include, forexample, rapid thermal chemical vapor deposition (RTCVD), low-energyplasma deposition (LEPD), ultra-high vacuum chemical vapor deposition(UHVCVD), atmospheric pressure chemical vapor deposition (APCVD) andmolecular beam epitaxy (MBE).

Referring now to FIG. 6, alternatively, growth of the epitaxial layer 62may continue until an extended epitaxial region 72 may be formed in anarea above the epitaxial layer 62 outside the spacers 32. Epitaxialgrowth in the extended epitaxial region 72 may generally take place on a{111} plane. The triangular shape observed in the extended epitaxialregion 72 may be a consequence of the different growth rates during theepitaxial deposition process inherent to each crystallographicorientation plane of the material forming the epitaxial layer 62. Inother embodiments, the extended epitaxial region 72 may have a shapeother than the triangular shape depicted in FIG. 6. In this embodiment,the extended epitaxial region 72 and the epitaxial layer 62 may formextended constrained source-drain regions 74.

The source-drain regions 64 (FIGS. 5-6) may be geometrically constrainedby the spacers 32 such that lateral epitaxial growth, particularly inthe {111} plane, may be prevented. This may allow for optimal finspacing and device density, reducing the amount of layout constraints inthe semiconductor structure 100 that may be dictated by the size of thelateral epitaxial growth. Also, by preventing lateral growth duringformation of the source-drain regions the risk of contacting anotherelectrical component and cause an electrical short in the device may bereduced.

Another embodiment by which to form constrained source-drain regions isdescribed in detail below by referring to the accompanying drawing inFIGS. 7-14. The present embodiment may include forming an etch stopliner above the fins prior to forming the constrained source-drainregions.

Referring now to FIG. 7, a nitride liner 118 may be conformallydeposited above the fins 14, according to another embodiment of thepresent disclosure. The nitride liner 118 may function as an etch-stopliner to protect areas of the substrate 10 located between the fins 14during subsequent etching steps. In the depicted embodiment, thesubstrate 10 includes a bulk silicon substrate in which the nitrideliner 118 may also protect STI regions 12 during successive etchingsteps. In general, the nitride liner 118 may prevent excessive over etchof areas of the substrate 10 located between the fins 14. The nitrideliner 118 may be formed by any deposition method known in the art suchas, for example, CVD or ALD of a nitride material. The thickness of thenitride liner 118 may vary from approximately 5 nm to approximately 25nm.

Referring now to FIG. 8, a dielectric layer 120 may be deposited on thesemiconductor structure 200. The dielectric layer 120 may include anysuitable dielectric material, for example, silicon oxide, hydrogenatedsilicon carbon oxide, silicon based low-k dielectrics, flowable oxides,porous dielectrics, or organic dielectrics including porous organicdielectrics and may be formed by any suitable deposition method known inthe art, for example, by CVD of the dielectric material.

The dielectric layer 120 may be planarized until a top portion of thenitride liner 118 positioned above the fins 14 is exposed. A chemicalmechanic polishing (CMP) may be conducted until the dielectric layer 120may be substantially coplanar with the top portion of the nitride liner118. Stated differently the CMP technique may be conducted until a topsurface of the dielectric layer 120 is substantially flush with a topsurface of the exposed portion of the nitride liner 118. The dielectriclayer 120 may remain above the substrate 10 and between the fins 14 inorder to protect these areas during subsequent etching steps.

Referring now to FIG. 9, a top portion of the nitride liner 118 (FIG. 9)may be removed to expose a top surface of the fins 14. The top portionof the nitride liner 118 (FIG. 9) may be removed by means of ananisotropic etching technique in which the etch rate in the directionnormal to the surface to be etched may be greater than in the directionparallel to the surface to be etched. The anisotropic etching techniquemay include a reactive-ion etching (RIE).

After exposing the top surface of the fins 14, the dielectric layer 120may be removed by means of any etching technique known in the art.

Referring now to FIG. 10, a gate 122 and a gate cap 128 may be formedfollowing the processing steps previously described in FIG. 2. It shouldbe noted that the formation of the nitride liner 118 prior to formingthe gate 122 may limit this alternate embodiment to a gate last orreplacement metal gate (RMG) process flow. Therefore, the embodimentdescribed below uses a gate last process flow.

In a gate last process flow, the gate 122 may include a dummy gate whichmay be pattered and etched from a polysilicon layer. A pair of devicespacers can be disposed on opposite sidewalls of the dummy gate. Thedummy gate and the pair of device spacers may then be surrounded by aninterlevel dielectric. Later, the dummy gate may be removed from betweenthe pair of device spacers, as by, for example, an anisotropic verticaletch process such as RIE. This creates an opening between the pair ofdevice spacers where a metal gate may then be formed between the pair ofdevice spacers. Optionally, a gate dielectric may be configured belowthe metal gate.

Referring now to FIG. 11, spacers 132 may be formed on opposite sides ofthe nitride liner 118. The formation of the spacers 132 may follow thesteps described above with reference to FIG. 3. In this embodiment, thespacers 132 may be adjacent to the nitride liner 118. For illustrationpurposes only, without intent of limitation, only the spacers 132 onopposite sidewalls of the nitride liner 118 are depicted in thedrawings.

Referring now to FIG. 12-12 a, the fins 14 may be removed following theprocessing steps previously described in FIGS. 4-4 a. In thisembodiment, the removal of the fins 14 may create a trench 144 betweenopposing sidewalls of the nitride liner 118.

Referring now to FIG. 13, an epitaxial layer 162 may be formed in thetrench 144 (FIG. 13). The epitaxial layer 162 may replace the fins 14(FIG. 12). The trench 144 (FIG. 13) between the opposing sidewalls ofthe nitride liner 118 may provide a template to re-grow fins in thesemiconductor structure 200 in a way such that lateral epitaxial growthmay not occur during formation of the epitaxial layer 162, and thereforeproducing laterally constrained source-drain regions 164. The epitaxiallayer 162 may be grown directly from the substrate 10 exposed at thebottom of the trench 144 (FIG. 13). In embodiments in which thesubstrate 10 is an SOI substrate, the epitaxial layer 162 may be growndirectly from a portion of the fins 14 (FIG. 12 a) remaining at thebottom of the trench 144 (FIG. 12 a). In such embodiments, the portionof the fins 14 remaining at the bottom of the trench 144 (FIG. 12 a) mayserve as a seed layer for growing the epitaxial layer 162.

The epitaxial layer 162 may include any suitable semiconductor materialhaving a dopant concentration according to the characteristics of thesemiconductor structure 200.

For example, in one embodiment where the semiconductor structure 200 isan n-type field effect transistor (n-FET) device, the epitaxial layer162 may include a carbon-doped silicon (Si:C) material, where the atomicconcentration of carbon (C) may range from approximately 0.2% toapproximately 3.0%. The epitaxial layer 162 may be doped by any knownn-type dopant use in the fabrication of n-FET devices such as, forinstance, phosphorus or arsenic. In one embodiment, the dopantconcentration in the epitaxial layer 162 may range from approximately5×10¹⁹ cm⁻³ to approximately 2×10²¹ cm⁻³.

For example, in another embodiment where the semiconductor structure 200is a p-type field effect transistor (p-FET) device, the epitaxial layer162 may include a silicon germanium (SiGe) material, where the atomicconcentration of germanium (Ge) may range from approximately 10% toapproximately 80%. The epitaxial layer 162 may be doped by any knownp-type dopant use in the fabrication of p-FET devices such as, forinstance, boron. In one embodiment, the dopant concentration in theepitaxial layer 162 may range from approximately 5×10¹⁹ cm⁻³ toapproximately 2×10²¹ cm⁻³.

Examples of various epitaxial growth process apparatuses that may besuitable for use in forming the epitaxial layer 162 may include, forexample, RTCVD, LEPD, UHVCVD, APCVD and MBE.

Referring now to FIG. 14, alternatively, epitaxial growth may continueuntil an extended epitaxial region 172 may be formed above the epitaxiallayer 162. Epitaxial growth in the extended epitaxial region 172 maygenerally take place on a {111} plane. The triangular shape observed inthe extended epitaxial region 172 may be a consequence of the differentgrowth rates during the epitaxial deposition process inherent to eachcrystallographic orientation plane of the material forming the epitaxiallayer 162. In other embodiments, the extended epitaxial region 172 mayhave a shape other than the triangular shape depicted in FIG. 14. Inthis embodiment, the extended epitaxial region 172 and the epitaxiallayer 162 may form extended constrained source-drain regions 174.

The source-drain regions 164 (FIGS. 13-14) may be geometricallyconstrained by the nitride liner 118 such that lateral epitaxial growth,particularly in the {111} plane, may be prevented. This may allow foroptimal fin spacing and device density, reducing the amount of layoutconstraints in the semiconductor structure 200 that may be dictated bythe size of the lateral epitaxial growth. Also, by preventing lateralgrowth during formation of the source-drain regions the risk ofcontacting another electrical component and cause an electrical short inthe device may be reduced.

Therefore, by cladding or confining the fins between sidewalls spacersor a nitride liner, epitaxial source-drain regions may be formed withconstrained lateral epitaxial growth. As a result, fin-to-fin proximitymay be reduced and device density may be enhanced while decreasing therisk of contacting another electrical component and cause an unwantedelectrical short in the device.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method comprising: forming a plurality of finson a substrate; conformally depositing a nitride liner above and indirect contact with the plurality of fins and the substrate; removing atop portion of the nitride liner above the plurality of fins to expose atop surface of the plurality of fins; forming a gate over a firstportion of the plurality of fins, a second portion of the plurality offins remains exposed; forming spacers on opposite sidewalls of thenitride liner on the second portion of the plurality of fins; removingthe second portion of the plurality of fins to form a trench betweenopposing sidewalls of the nitride liner; and forming an epitaxial layerin the trench, wherein lateral growth of the epitaxial layer isconstrained by the nitride liner to form constrained source-drainregions.
 2. The method of claim 1, further comprising: depositing adielectric layer above the nitride liner; polishing the dielectric layerto expose a top portion of the nitride liner; and removing thedielectric layer.
 3. The method of claim 1, wherein forming theepitaxial layer comprises: epitaxially growing an in-situ dopedsemiconductor material including silicon or silicon-germanium.
 4. Themethod of claim 1, wherein the substrate comprises a bulk semiconductorsubstrate or a semiconductor-on-insulator (SOI) substrate.
 5. The methodof claim 1, wherein removing the second portion of the plurality of finsto form the trench between the spacers comprises: removing an upperregion of the second portion of the plurality of fins while a lowerregion of the second portion of the plurality of fins remains in thetrench, wherein the lower region of the second portion of the pluralityof fins provides a seed for growing the epitaxial layer on SOIsubstrates.
 6. The method of claim 1, further comprising: forming anextended epitaxial region directly on top of the epitaxial layer andabove the trench.
 7. The method of claim 6, wherein the extendedepitaxial region comprises epitaxial growth on a {111} plane.
 8. Themethod of claim 6, wherein the extended epitaxial region comprises atriangular shape.
 9. A structure comprising: a plurality of fins on asubstrate; a gate over a first portion of the plurality of fins, whereina second portion of the plurality of fins not covered by the gatecomprises an epitaxial layer geometrically constrained by a pair ofspacers located on opposite sidewalls of the second portion of theplurality of fins; and a nitride liner located between the pair ofspacers and the second portion of the plurality of fins, wherein thenitride liner further constrains the second portion of the plurality offins.
 10. The structure of claim 9, wherein the epitaxial layercomprises an in-situ doped semiconductor material.
 11. The structure ofclaim 9, wherein the nitride liner comprises an etch stop to preventover etch of substrate areas located between the plurality of fins. 12.The structure of claim 9, further comprising: an extended epitaxialregion directly on top of the epitaxial layer, wherein the extendedepitaxial region has a triangular shape.